It is generally recognized that magnetic recording discs provide relatively economical means for storing data and are in data processing systems. The discs in current use are frequently flexible. A flexible disc is preferable over a rigid disc in that it is less expensive to produce. The flexible discs currently in use are flat. This configuration may cause problems.
Briefly stated, the problem with a flat flexible disc is that when it is rotated about an axis, the outer region of the disc may be destabilized by any perturbation in the air flow. Since the disc by its very nature is flexible, the destabilized section of the disc will tend to flutter. The flutter in turn makes it impossible to maintain the tolerances needed for reliable recording and retrieving of data.
The problem of flutter has been addressed by Hoshina in U.S. Pat. No. 3,863,266 in which he teaches that a flat disc may be stablized by supplying constant air pressure to the underside of the disc. To maintain constant air pressure on the underside of the disc a backing plate is used. This backing plate is so configured that the spacing between the backing plate and the disc decreases as one moves from the center to the periphery of the disc. Air flows from the center to the periphery of the disc. A constant air pressure is maintained on the disc by compensating for the decrease in the radial flow by decreasing the separation between the backing plate and the disc. While this attempt at a solution allows one to stabilize a single flat disc, it will not provide for the stabilization of a series of stacked discs since each disc must be immediately adjacent to a backing plate. Furthermore, this stabilization technique allows information to be retrieved from only one side of the disc. To access the second side of the disc will require remounting of the disc.
Ewert et al in U.S. Pat. No. 3,830,506 teach the stabilization of a flexible disc by employing a curved backing plate. The backing plate induces curvature into the disc and this curvature tends to stabilize the disc. However, as in the case of Hoshino, this solution is limited to the stabilization of a single disc and furthermore the design does not readily lend itself to retrieving information from both sides of a disc.
While Hoshino and Ewert et al have addressed the problem of stabilization of a single flexible disc, they do not treat the more complex problem of stabilizing a disc while maintaining the ability to store and access information from a series of stacked discs. Wadey in U.S. Pat. No. 3,090,626 teaches the use of a bistable disc support means that will allow data to be stored and retrieved from either side of a series of stacked rigid flat discs. However, to practice the teaching of Wadey, the discs must be rigid for the following reasons. First the disc must be rigid to transmit the force applied normal to the edge of the disc to the support means; the transmitted force changes the position of the aforementioned bistable support means and allows access to an adjacent disc. Second the disc must be rigid so that its edge will not flutter during rotation. Flutter as was mentioned earlier will make the outer portion of the disc unacceptable for storing and retrieving information.
While the prior art has offered several partial solutions to the problems of stabilizing and accessing magnetic discs, there is a continuing need for an inexpensive, self-stabilizing flexible magnetic disc suitable for use in single disc applications as well as in disc packs.